Telephone system



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min .J/ N nm. NLQL.. .1.- L xQ @ML W Q bmw, MW@ @L New Nmmwlr 1% f2@ S Patented Jan. 30, 1940 UNITED STATES FFICE TELEPHONE SYSTEM Appiicaticn February 25, 1937, Serial No. 127,617 In Germany March 6,-1936 24 Claims.

In automatic telephone systems the cost of .the devices individual to each subscribers line plays an important part in the total cost of the system. Accordingly it is desirable to re-use devices already on hand, particularly subscribers lines when erecting new exchanges or extending systems already in existence. In the case of exchanges adapted for loop impulsing dificulties are involved with lines having a high resistance or leakages. It has therefore been proposed to Voperate with alternating current in the case of such subscribers lines while the usual operation with exchange battery is employed for lines which are in good condition.

Such a non-uniform mode of operation which naturally can also be employed for new systems if lvery long subscribers lines are involved, is made possible in a simple'manner according to the invention and without the provision of special devices n the exchange for each type of diferently equipped subscribers line.

This is achieved in that the subscribers stations disposed in lines having a high resistance or leakages are arranged for induced current impulsing and devices serving to receive the induced impulses are so arranged in the exchange devices which are likewise accessible to subscribers lines employing loop impulsing that an impulse receiving relay, which is under the inuence of the impulse circuit in the case of calls from. subscribers stations employing loop impulsing, is brought under the influence of the devices for'receiving the inducedimpulses in the case of calls-from subscribers stations employing induced current impulsing, which receiving devices receive the induced impulses transmitted from the calling station and transmit these to the impulsing receiving relay for normal impulses in correspondence with the interruptions in the loop at the calling station.

The present invention alsorelates-to a circuit for an impulse receiving device for systems in vwhich numerical impulse receivers are set by the transmission of induced impulses.

In the case of the transmission of induced impulses an impulse to be transmitted is determined by a disconnecting .and a connecting impulse or by a connecting and rdisconnecting impulse on the primary side of the repeater. Thus for each impulse transmitted two successive. impulses in opposite directions operate on the ,secondary side of the repeater.

, Such impulses can seldom be transmitted with the desired uniformity as regards their length, strength and time displacement on account of the conditions of operation which have to be considered in the case of a system such as that .under consideration.

The invention relates to an impulse receiving deviceV for receiving and repeating induced impulses .which is insensitive as regards the above Ashortcomings and effects eiicient reception of the induced impulses and their transmission and yconversion to normal current impulses without necessitating specialfconstruction.

This is achieved in that by the individual successive induced impulses two impulse receiving relays for receiving and repeating the impulses .are alternately brought under the influence of the impulse circuit.

An embodiment of the invention is illustrated in the drawing, but the invention is not to be considered limited to this embodiment. T11l represents a subscribers station, the devices of vwhich are so arranged that on initiating a call c a loop is established whereupon impulses are transmitted as normal D. C. impulses when the loop is interrupted. Tn! represents a subscribrers station at which on initiating a call an induced impulse is transmitted whereupon on subsequently operating the dial, induced impulses are transmitted for setting succeeding numerical impulse receivers. AS represents a call finder whichhas access both to subscribers stations employing loop impulsing and also to subscribers e stations employing inductive impulsing. -Similarly, over the final selector LW variously 4equipped subscribers stations can be reached.

When the subscriber at station Tn takes up his receiver relay R is energized over the leads :.1

La and Lb. Relay R operates its contacts and at contact lr, characterizes the calling subscriber in the contact bank of the testing wiper ascy of the call nder. Contact 2T sets up a start circuit over which relay An is energized in the following` circuit: earth, battery, resistance Wi, con- .tacts 1,21', Zit, relay An, earth. Relay An energizes relay R2 in the following circuit earth, contacts 3cm, Hp, relay R2, battery, earth. Relay R2 prepares the testing circuit of the call finder at contact5r2. At contact M2 the rotary magnet Das of the call'nder is operated in the following circuit: earth, interrupter Un, contact 412, rotary magnet Das, contact 8p, battery, earth. When the callrinder finds the calling line the following circuit is. established for relays P and T: earth, contact 512, windings II and I of relay P, wiper asc, contact IT, relay T, battery, earth. Relays P and Tenergize. Contact 979 establishes acircuit passing over contact 48112 sorthat an- Alill other hunting call finder cannot be set on the line of subscriber Tn. Contact Ip energizes relay V. Contacts 6p and 1p switch the speaking leads La, Lb, through. Contact |210 prepares the testing circuit of the nal selector which passes over the winding of relay P2. Contactl |3p applies earth in preparation to contact 5|a. Relay T on energizing operates contacts |8t, |9t, 2015 and 2|t. Contact 20t maintains the guarding circuit established by the testing of the call finder independent of contact lr. Contact 2|t breaks the circuit for the start relay An so that this releases in the event of no other call occurring. Contact 30m is accordingly opened. After relay T has energized contact llp disconnects relay R2 so that this restores contacts 412 and 5r2 to normal.

When the speaking leads are switched Athrough by contacts 6p and 'ip relay J is brought under the iniluence of the loop at station Tn. Relay J accordingly energizes in the following circuit: earth, battery, relay J, contact 46g, winding I of the repeater Ue, contact 5p, wiper asa of the call finder, lead La, the loop at station Tn, lead Lb, wiper ash of the call finder, contact "1p1, winding III of the repeater Ue, contact 45g, chokecoil Drl, earth. Relay J operates its contacts and energizes relay V1 over Contact IM. Contact |37 prepares the circuit for relay H so that this energizes when Contact |512 closes and by opening contacts lh prevents relay G from energizing over winding II. Contact Viti maintains the `guarding circuit passing over Contact 9p. Relay V1 does not release during the impulse transmission. Contact 49121 serves to energize relay V2 which switches over contact 48212.

Relay J which is energized over the subscribers loop after the call iinder has switched through deenergizes impulsively in response to the operation of the dial at the subscriber's` station Tn. On the rst impulse which is transmitted in any desired manner to a driving magnet of the iinal selector LW the off-normal contact Ict is switched over so that when relay H is impulsively operated by contact |311' relay G cannot energize over Contact |6h and its winding II.

When the final selector is stepped to a subscribers line for example that of station T113, by the impulses transmitted from the calling station. If the desired line is free relay P2 energizes in the following circuit: earth, contacts |21, windings II and I of relay P, wiper ic, and devices in the desired subscribers line which are not shown. Relay P2 switches the speaking leads through at contacts 23112 and Mp2. Contact 25112 establishes a guarding circuit which passes from earth over contacts |2111 and 25112, winding I of relay P2 and wiper Ic. Contact 255132 connects wiper ld of the final selector to earth. However, assuming that the desired subscribers station is adapted for loop impulsing relay M does not energize since wiper ld has been set on a contact to which relay M is not connected. Ringing current is now transmitted to the called station in the known way. When the called party takes up his receiver relay Se energizes in the following circuit: earth, battery, relay Se, contact 23m, winding II of the repeater Ue, contact 23102, wiper la, of the nal selector, the loop at the subscribers station TuS, wiper lby of the nal selector, contact 24192, winding IV of the repeater Ue, contact 29m, choke-coil DTZ, earth. Relay Se is operated and disconnects ringing current in any known manner. When the speaking connection is established the subscriber at T11-3 is enabled to cause relay Se to release and reenergize by transitorily hanging up his receiver so as to enable him to signal, for example to a supervisory operator. The release of a call is under the influence of the calling party in the present embodiment.

If the nal selector LW is set on a subscribers line adapted for transmitting induced impulses relay M is operated over the common wiper ld after the nal selector has tested and reiay P2 has energized and closed Contact 267:2. Relay Se is thereupon disconnected from the speaking leads through the switching over of contacts 28m and 29m. Relay D is brought under the iniiuence of the called station by contacts 27m. Contact 36m prepares an energizing circuit for relay F. When the called party takes up his receiver relay D is operated by an induced impulse generated at the subscribersl station when the receiver is removed. This induced impulse is generated by a device similar to that represented at subscribers station Tnl. The impulse passes from the device at the subscribers station over wiper la., contacts 23112, 21m,

energizing of relay F in the following circuitf earth, contacts 39m, Sid, relay F, battery, earth. Relay F operates its contacts and at contact 35j applies earth to the relay Se, which interrupts the transmission of ringing current in the manner already described. When the induced iin-5Y- pulse transmitted when the party at station Tn takes up the receiver, has died down relay D releases. The following locking circuit is established for relay F: earth, contacts 353m, 3Id (restored), 38e, 33j, relay F, battery, earth. Relay E is now connected between the speaking leads over contact 34j and the relapsed contact 32d, so that a second induced impulse generated when the called station replaces the receiver influences relay This causes relay F to deenergize on account of the opening of contact 38e and relay Se is deenergized by the opening of contact 351. When this induced impulse dies down relay F is not energized againl when relay E releases since in the meantime contact 33j has opened. Relay D is now disposed between the speaking leads so that if the receiver at the subscribers station is taken up again relay D and consequently also relay F energize, with the result that relay Se energizes again. In this way the called station is enabled to transmit a icker signal.

If the call is to be released the subscriber at station Tn replaces his receiver. This results in deenergizingv relay J and the slow operating relay VI. Relay Vl opens contacts Hol so that relay P releases. Contact 911| breaks the circuit for the slow relay V2, which makes a delayed release so that contact 48122 only restores to normal after the guarding circuit has been opened at contact 9p. The guarding circuit passing over winding I of relay P2 is also broken by the release of relay P at contacts |220. Relay PZ releases and effects the restoration of the nal selector LW to the normal position in any known manner. When relay P released contact Hp wasalso restored to normal so that after relay T has released the call nder AS can once more be seized.

When the subscriber at station Tnl initiates Eas a call the switchhook contacts Hul and I-Iu'2 are operated when the receiver is removed. The switchhook contact Hui disconnects the bell W from the speaking leads and connects up the `subscribers apparatus, repeater G, microphone M, and telephone F. On account of the switching over of contact IIu2 relay K is energized in the following circuit: positive pole of battery B, contact 2s, relay K, contact usa, which is only switched over when the dial plate is off-normal, switch-hook contact Hu2, and negative pole of battery B. Relay K operates its contacts, contact 4k closing before contact 5k. This prevents the make impulse from being transmitted inductively over the leads Lc! and Lbl. Contact 3k operates relay S over positive pole of battery B, relay S, contact 3k, switchhook contact I-Iu2, negative pole of battery B. Contact ls breaks the circuit passing over winding I of the transformer Tr, so that the rst break impulse isl transmitted. Relay K releases since it is shortcircuited by the energizing of relay `S over negative pole of relay B, contact ls, relay K, contact nsa, switchhook contact I-Iu2, and negative pole of battery B. Relay S remains energized over the positive pole of battery B, relay S, resistance contact Is, negative pole of battery B. The rst induced impulse passing over the line Lal/Lb! energizes relay Rl over winding I. Relay Rl accordingly operates its contacts so that the following circuit is established for relay An over contacts drl and the following locking circuit for winding II of relay Rl: earth, battery, winding II of relay Rl, contacts dilrl, 4315i, relay An, earth. Relay R! remains energized over its winding II after the induced impulse energizing relay RI over winding I has died down. Contact 39N characterizes the calling line at wiper ascof the call finder AS. On the closing of contact San earth 'is applied to line LL thereby starting up a free call finder. If the call finder AS which is represented in the drawing, is free, contact l lp i will be in the normal position so that on closing contact 3cm the following circuit is established for relay R2: earth, contacts 3cm, Hp, relay R2, battery, earth. Relay R2 operates its contacts and starts the call finder shown in the drawing over Contact 41:2. The testing circuit of the 'call finder is prepared at contact ST2. When the call iinder finds the calling subscribers line the following testing circuit is set up: earth, contact 512, windings II and I of relay P, contact 38M, relay TI, battery, earth. In this circuit relays P and TI energize. Relay P brings the call finder to rest by opening contacts 8p. In addition it establishes a guarding circuit by closing contact 9p and connecting earth directly to winding I of relay P over contact 4802 and contact 9p. Relay R2 is caused to deenergize by contact lip. Contacts 6p and 7p switch the connecting line through. Through the energizing of relay 'Il winding I of relay Rl is disconnected by contact dipl. Contact 42H maintains the'guarding circuit independent of contact 39H. Contact 431i! deenergizes winding II of' relay Rl. If no further impulse is received to maintain relay An energized this relay releases and opens contact When the connecting line is switched through at contacts '5p and 'lp no circuit is established for relay J over the loop at the calling station since the condenser Ko is disposed in the upper speaking lead thereat.

Since relay J does not energize when the line is switched through relay G operates over winding l1 in the'following circuit when contact l5?) tion.

closes as a result of relay V operating on the closing of contacts mp: earth, contact |517, 01T- relay J is operated in the following circuit: earth,

contacts |310, 51a, 51h, 540,46@ relay J, battery, earth.` Relay J operates its contacts and by closing contact E47" energizes relay VI. The guarding circuit for the call iinder passing over contacts c3112 is maintained by the closing of contact HUI before the opening of the contact 48112. Contact 419e! energizes relay V2. Contact 48122 is switched over but does not promote any switching opera- Relay A was connected to the speaking leads of the connecting line by Mg.

The subscriber can now be notified that he can commence to dial by the transmission of an vexchange signal in any known manner. When the subscriber operates his dial switch for the purpose of setting succeeding numerical impulse receivers contact nsa is switched over when the dial is drawn olf-normal. Relay K accordingly energizes over the positive pole of battery B, contact 2s, contact nca, relay K, contact ls, and negative pole of battery B. Contact k connects winding II of the transformer T1' to lead Lal. As the dial plate runs back contact nsa remains closed while contact ns1' is intermittently operated. When thev circuit is completed for the first time by contact ns1' an impulse is inductively transmitted over leads La! and Lbi and is taken up by relay A. Relay A operates its contacts and vby switching over contact 55a deenergizes relay J- and energizes relay C in the following circuit: earth, contacts 83p, Ela, relay C, battery, earth.

Contact 50a establishes a locking circuit for relay A which is vmaintained until the induced impulse has died down. Contact 53o opens the original energizing circuit for relay A. When relay A releases relay-C remainsoperated in the following circuit: earth, contacts i339, Sla., Elib, 5de, relay C,

battery, earth. On the release of relay A relay B is connectedtothe speaking lead by contact 50a.'

which restores to normal. When now another induced impulse is transmitted on the opening of contact usi this is taken up by relay B whereupon relay J .which released when contact Sla was switched over, again energizes. This circuit for relay J passes from earth over contact |311, Bla, 51h, Mig, relay J, battery, earth. When the induced impulse has died down relay J remains energized over earth, contacts 1312,. Ela., 51D, 54e, 46g, relay J, battery, earth. Subsequent impulses are` transmitted to relay J in the same way through the alternate operation of relays A and B. Relay J by releasing and reenergizing is utilized to control the final selector LW in the known manner. The nal selector is stepped Vby this transmission of impulses in the manner already described and its operation is adapted to suit the equipment of the called station by the aid of relay M. When the dial plate at the calling station Til/l has returned to normal, contact 'usa is restored to its original position. Relay K is accordingly deenergized since it issliort-circuited by the following circuit: negative pole of battery B, contact ls, relay K, contact nsa in its normal position, switch-hook contact Hu and negative pole of battery B. Reiay K then' disconnects winding II of the transformer Tr by contact 5k so that the subscribers who'are now connected lare consequently restored to normal.

'is accordingly closed at contact is.

vcontact Ict is lrestored to normal.

together can converse. W'hen the connection is to be released subscriber Tn! replaces his receiver. The switchhook contacts Hui and Hu2 The following circuit is established for relay K: positive pole of battery B, contact 2s, switchhook contact Hu2, contact nsa, relay K, contact is, negative pole of battery B. In this circuit relay K energizes so that winding II of the transformer Tr is again connected to lead Lal. Contact 3k shortcircuits relay S in the following circuit, positive pole of battery B, relay S, contact 3k, switchhook contact Hui', contact 2s, positive pole of battery B. Relay S releases. The energizing circuit provided for winding I of transformer Tr This energizing of winding I of transformer Tr promotes the transmission of an induced impulse to relay A. Relay A energizing and over earth and contacts i319 and 5m operates relay C. Relay C energizes and locks up over contact 56o in a circuit which becomes operative when contact 51a, is restored to normal when the induced impulse has died down. The energizing of relay A deenergizes relay J. At contact hij relay J breaks the circuit for relay Vl. Relay V releases and at contact HUI breaks the guarding circuit in which relays P and T were held energized. Relays P and T release. The circuit for relay V2 is broken at contact 4911i. When this connects earth to contact 9p over contact 48122 the former contact is already opened so that the release can proceed unhindered. On the release of relay P the circuit for relay V is opened at contact lfpand the circuit for relay C is opened at contact 43p. Relays V and C release. Relay J remains deenergized. Contact i210 breaks the locking circuit for relay P2 so that this also restores to normal. The switch LW releases in known manner whereupon On the opening of contact |512 relay G also releases.

After the transmission of the make impulse which serves as a release impulse by the deenergizing of relay S relay K also releases since the negative `potential of the battery B is disconnected at Is. The induced impulse produced on the opening of contact 4k is not transmitted since contact 5k leaves its operated position before contact 4k.

As has been described, in the present embodiment the special construction of the station Tnl is characterized by the energizing of relay G. The energizing of relay G is promoted by the condenser Ko disposed in the upper speaking lead. This relay could alternatively be operated over a special wiper of the call nder as soon as the call nder becomes set on a subscribers line employing induced impulse transmission. Relay G must then be similarly connected as is relay M in the iinal selector LW.

What is claimed is:

l. In a device for controlling automatic switches, a controlling relay, intermediate controlling means, a line incoming to said device, means for seizing said line and transmitting impulses thereover to operate said relay, said relay connected directly to said line and responsive to received impulses under one condition of seizure, and means eiective under another condition of seizure for bringing said relay under control of said intermediate means and causing said intermediate means to respond to received impulses to in turn control said relay.

2. In a device for controlling automatic switches, a controlling relay, intermediate controlling means, a line incoming to said device, means for seizing said line and transmitting impulses thereover to operate said relay, said relay connected directly to said line and responsive to received impulses under one condition of seizure, means effective under another condition of seizure for bringing said relay und-er control of said intermediate means and connecting said intermediate means to said line to operate said relay responsive to one received impulse and to release said relay responsive to the succeeding received impulse.

3. In an automatic switching control system, stations of one class having means for transmitting alternating current impulses over their line circuits, stations of another class having means for transmitting direct current impulses over their line circuits, switching equipment having two impulse receiving means, means for associating the line circuit of a station of either class with said switching equipment, means responsive to the association of the line circuit of a station of said one class with said switching equipment for causing said line circuit to assume control of the rst said impulse receiving means, means responsive to the association of a line circuit of a station of said other class with said switching equipment for causing said last line circuit to assume control of the second said impulse receiving means. i

4. In an automatic telephone system, tw classes of subscriber stations and line circuits therefor, means at each station of one class for interrupting the associated line circuit to transmit impulses thereover, means at each station of rst said impulse receiving means, means effective when the line circuit of a station of said' 5. In an automatic switching control system,

stations of one class having means including impulsing contacts for transmitting over their line circuits two impulses for each operation of said contacts, stations of another class lhaving means including impulsing contacts for-transmitting over their line circuits one impulse for each operation of said contacts, switching equipment including automatic switches, switching control means, and intermediate control means, means for associating the line circuit of a station of either class with said switching equipment, means responsive to the association of the line circuit of a station of said one class with said switching equipment for placing said switching control means under control of said intermediate means and for placing said intermediate means under control of said line circuit, means effective upon the association of a line circuit of a station of said other class with said switching equipment to cause said last line circuit to assume the direct control of said switching control means, said switching control means effective to operate said automatic switches in correspondence with the impulsing contacts at a station of either class when the line circuit of -that Station is associated with said switching equipment. l

6. In an automatic switching control system, two classes of stations and line circuits therefor, means at stations of one class for interrupting their lino circuits to transmit impulses thereover, means at stations of the other class for transmitn ting impulses over their line circuits without interrupting said line circuits, switching equipment, means for extending the line circuit of a station oi either class to said equipment, one impulse receiving means connected to the line' circuit responsive to the extension thereof tosaid switching equipment, said impulse receiving means controlled directly hy impulses received over said line circuit if said line circuit is that of a station of said one class, and an intermediate impulse receiving means connected to the line circuit responsive to the extension thereof to said equipment if said line circuit is that of a sta-y tion .of said other class, said intermediate im`- pulse receiving means eiective to control said one impulse receiving means in accordance-With the received impulses.

'7. In an automatic switching control system, two classes of stations and line circuits therefor, impulse generating means of one kind at each station oi one classfor transmitting :over its associated line circuit impulses of a certain character, impulse generating means. of another kind at each station of the other class for transmitting over its associated line circuit impulsesof a different character, switching equipment including a line impulse receiving relay, means for connecting the line circuit of a station of either class to Said line relay, and means for energizing said line relay over said connected line circuit only when said connected line circuit is one which is associated with a station of said other class.

8. In an automatic switching control system,` two classes of stations and line circuits therefor,

impulse generating means of one kind at each station of one class for transmitting over its associated line circuit impulses of a certain character, impulse generatingmeans of another kind at each station of the other class for transmitting over its associated line circuit impulses :of-a clifferent character, switching equipment including a line impulse receiving relay and other impulse receiving means, means for connecting the line circuit of a station of either class to said line relay, means for energizing the line relay over the connected line circuit only whenI said connected line circuit is one which is associatedwith a station of said one class, and means for disconnecting said line relay from said lin-e circuit, for connecting said other impulse receiving means to said line circuit andfcr placing said line relay under control of said other impulse receiving means when said connected line circuit is other which is associated with a station lof said one class.

9. In a system such as that claimed in claim '7, other impuls-e receiving means, means effec-tive a-predetermined length ci time after the conneotion of a line circuit oa station of either class to said line relay to disconnect said line relay from said line circuit and to connect said other impulse receiving means to said line circuit, said last means rendered ineilective by the prior energization of said line relay over the connected line circuit only when said connected line circuity is one which is associated with a station of said other class.

10. In an automatic switching control system;

cuits therefor, means at stations of one class for interrupting their line circuits to transmit impulses thereover, means at stations of the other class for transmitting impulses over their line circuits'without interrupting said line circuits, switching equipment including a line impulse receiving relay and .other impulse receiving means, means for associating the line circuit of .a station of either class with said switching equipment, automatic discriminating means eective responsive to. the association of the line circuit of either class with said switching equipment to determine if said line Vrelay shall .be connected to said line circuit, or7 alternatively, if said other one class of line circuits effective to conduct direct current, another class of line circuits effective tc conduct only current' to which va condenser is transparent, discriminating means including a Iline relay, means for causing a line circuit of either class to complete a series circuit includingA the winding of said relay and a .source of direct current, impulse receiving means, and means effective a predetermined interval of time after the connection of a line circuit of a station of either class t0 said line relay for disconnecting said line relay from said line circuit and connecting Said impulsereceiving means to said 'line circuit, said last means rendered ineffectivev by the prior energiza-tion of said line relay over the connected line circuit whenv the connected line circuit is one which conducts direct current.

13. In a telephone system, one class of subscribers line circuits effective to conduct direct current, another class of subscribers line circuits eiiective to rconduct only current to which a condenser is transparent, automatic switches, means including one of saidautomatic switches for extending a connectionto a subscribers line circuit of either class, a relay for operating in correspondence with the switchhook of the subscribers substation to which last said line circuit extends, intermediate controlling means, means effective under one condition for controlling said relay directly from two classesl of controlling stations and'line cirsaid last line circuit, means elective under/an alternative condition for placing said relay under f for transmitting impulses of current to which a condenser is transparent over their line circuits,

means for transmitting impulsesof direct current over their line circuits, exchange equipment including a line impulse receiving relay and other impulse receiving means, automatic means v responsive to the initiation of a call from a substation vof either class for associating the line circuit of said 4substation with said exchange equipment, means responsive to the association 0f the line circuit of a substation of said one i5 subscribers substations of another class having class with said exchange equipment for placing said line relay under the control of said other impulse receiving means and for placing said other impulse receiving means under control of said line circuit, means effective when the line circuit of substation of said other class is associated with said exchange equipment to cause said last `line circuit to assume the direct control of said line relay.

15. In a system such as claimed in claim 14, wherein said other impulse receiving means includes a pair of relays and means controlled conjointly thereby for connecting said pair of relays alternately to said line circuit.

16. In a system for controlling automatic switches, a line circuit, means for transmitting over said line circuit impulses of current to which a condenser is transparent, impulse receiving means including two line relays and means for connecting said line relays alternately to said line circuit, said impulse receiving means eiiective to control the transmission of direct current impulses to said automatic switches.

1'7. In a signalling system, a line, means for transmitting impulses thereover, a pair of impulse responding devices associated with the line and energized alternately thereover by successive ones in a train of impulses, an electrical circuit to be controll-ed, and means controlled conjointly by said devices for completing said circuit responsive to each energization of a particular one of said devices and for interrupting said circuit responsive to each energization of the other device.

18. In a signalling system, a transformer, means for impressing voltage of a normal value upon the primary winding of said transformer, means for causing the normal value of the impressed voltage to be departed from for an interval of time, a pair of signal receiving devices, and

a line circuit for said devices including a secondary winding of said transformer, the first of said devices responsive to current induced in the line circuit by the departure of said impressed voltage from said normal value, the `second of said devices responsive to current induced in the line circuit by the reversion of said impressed voltage to said normal value at the end of said interval of time.

19. In a signalling system, a circuit to be controlled, controlling means including, a transformer, means for impressing voltage of a normal value upon the primary winding of said transformer, means for causing the normal value of the impressed voltage to be departed from for an interval of time, a pair of signal receiving relays, and a line circuit for said relays including a secondary winding of said transformer, the first of said relays energized by current induced in the line circuit by the departure of said impressed voltage from said normal value to complete said first circuit, the second of said relays energized by current induced in the line circuit by the reversion of said impressed voltage to said normal value at the end of said interval of time to interrupt said rst circuit.

20. In a system for controlling automatic switches, a completed line circuit, means for transmitting impulses over said line circuit without interrupting the continuity thereof, impulse receiving means including two relays, means for connecting rst said relay to said line circuit to operate responsive to an impulse transmitted over said line circuit, said first relay eifectiveto prepare second said relay for operation, said second relay operated responsive to the succeeding impulse transmitted over said line circuit and effective to prepare said iirst relay for reoperation, said impulse receiving means eiective to control the transmission of direct current operating impulses to said automatic switches.

2l. In a system for controlling automatic switches, a line circuit, another circuit inductively associated therewith, a source of current for said other circuit, means for interrupting said other circuit to effect thel transmission of impulses over said line circuit, impulse receiving means including three relays, means for connecting first said relay to said line circuit to operate responsive to an impulse transmitted over said line circuit, said ist relay effective to operate said second relay, said second relay eiiective upon operating to interrupt the operating circuit of said rst relay and to prepare said third relay for operation, said third relay responsive to the succeeding impulse transmitted over said line circuit and effective to release said second relay, said second relay eiiective upon release to interrupt the operating circuit of said third relay and to prepare said rst relay for reoperation, said impulse receiving means effective to control the transmission .of direct current impulses to said automatic switches. v

22. In a system such as that claimed in claim 21 in which said first relay is also effective upon operating responsive to an impulse transmitted I over said line circuit to establish a locking circuit to keep itself operated for the duration of the impulse, and said third relay is also effective upon operating responsive to an impulse transmitted over said line circuit to establish a locking circuit to keep itself operated for the duration of the impulse.

23. In a system such as that claimed in claim 2l, in which said first relay is also eiective upon operating responsive to an impulse transmitted over said line circuit both to establish a locking circuit to keep itself operated for the duration of the impulse and to interrupt the operating circuit of said third relay, and said third relay is also effective upon operating responsive to an impulse transmitted over said line circuit both to establish a locking circuit to keep itself operated for the duration of the impulse and to interrupt the operating circuit of said first relay.

24. In a system such as that claimed in claim 20, in which the length of time between the operation of the rst said relay and the second said relay determines the length of the transmitted operating impulse, and the length of time between successive operations of either one of said relays determines the frequency of said transmitted operating impulse.

EDUARD WOCHINGER. 

